Dual Mass Flywheel (DMF)

Long Travel Damper Dual Mass Flywheel

Valeo’s Long Travel Damper Dual Mass Flywheel (LTD DMF) offers improved acoustic comfort and reduces vibrations. The LTD DMF significantly reduces perceived vibrations and engine noise. This represents a major step forward in powertrain filtration technologies. This technological improvement is especially important because the latestes engines with improved fuel consumption have higher torque and, consequently, generate greater vibrations, especially at low speed. The LTD DMF absorbs torque vibrations generated by the engine to the transmission, thereby increasing the comfort of the vehicle’s occupants.

Dual Mass Flywheel (DMF) Long Travel Damper (LTD)

Image: Dual Mass Flywheel (DMF) Long Travel Damper (LTD)
Credit: Valeo

A – engine side
B – transmission side
1 – drive plate No. 1
2 – hysteresis washer
3 – drive plate with springs
4 – back plate
5 – drive plate No. 2

The LTD technology is based on two sets of three springs operating in series and synchronised by a back plate. The straight springs are less sensitive to the centrifugal load than the curved springs. This provides less friction, hence the filtering is better than with the curved springs.

In addition to the known dual mass flywheel technology, the LTD DMF integrates a long travel damper developed by Valeo for torque converters in automatic transmissions (AT). This combination allows it to provide optimal filtration, especially during engine start-up, thanks to a maximum angular displacement of 80 deg, as well as an exceptional performance level in all engine regimes.

Valeo’s long travel damper dual mass flywheel offers comfort levels previously unknown on the most fuel-efficient engines. The NVH (Noise Vibration Harshness) level and ease of gear changes offer remarkable driving comfort for the most vibration-prone engines.

LTD DMF - no load

Image: LTD DMF – no load
Credit: Valeo

LTD DMF - under load

Image: LTD DMF – under load
Credit: Valeo

Flexible flywheel

The crankshaft bends under the force of the strong combustion pressure inside the engine cylinders. This generates the deflection of the crankshaft and an axis wobbling on the flywheel, which is bolted at the end of the crankshaft. Mechanical stress occurs between the bearings and crankshaft, generating vibrations. If not filtered, the result is a roaring noise caused by the engine, a flywheel axial vibration and a potential increased vibration at the clutch pedal.

Advantage of flexible flywheel

Image: Advantage of flexible flywheel
Credit: Valeo

The flexible flywheel filters the axial vibrations transmitted through the engine crankshaft. This is achieved by adding a flexible plate at the engine side of the flywheel mass. Deformation of the crankshaft continues, but it is not transmitted to the flywheel thanks to the flexible plate.

Advantages of the flexible flywheel:

  • reduced engine noise at high engine speeds
  • reduced bending stress on the crankshaft
  • reduced level of vibration on the clutch pedal
Flexible flywheel

Image: Flexible flywheel
Credit: Valeo

A – crankshaft side
B – clutch side

Flexible Long Travel Damper Dual Mass Flywheel

The flexible function can be present both on the rigid flywheel and on the Dual Mass Flywheel. On a DMF, the flexible plate is attached to the primary flywheel and a multi-stage hub is used to reduce the pressure in the crankshaft fitting bolts.

Flexible long travel damper dual mass flywheel

Image: Flexible long travel damper dual mass flywheel
Credit: Valeo

1 – flexi-plate
2 – primary mass
3 – curved springs & spring guides
4 – Long Travel Damper
5 – cover
6 – starter ring
7 – secondary mass

DMF for DCT

The flywheel used in the double clutch transmissions (DCT) is a special form of the LuK DMF. As in the conventional DMF in manual gearboxes, there is a primary and a secondary side. However the secondary side, in contrast to the conventional DMF, is not a fixed part of the DMF, so it is not designed as a flywheel mass but in the form of a drive plate. It serves only as a connection between the primary mass and the double clutch.

The secondary mass is replaced in this case by the weight of the double clutch, which is fitted on an input shaft (hollow shaft) of the gearbox. There is also no need for the direct bearing connection of the opposed masses, which is realised in the form of ball or plain bearings in the conventional DMF.

Standard DMF - for DCT

Image: Standard DMF – for DCT
Credit: LuK

1 – primary mass with arc spring
2 – drive plate with internal toothing to engage with the coupling wheel of the double clutch
3 – tension ring
4 – cover for primary mass with starter ring gear

The flywheel used in a DCT is a special form of the DMF. As in the conventional DMF in manual gearboxes, there is a primary and a secondary side. However the secondary side, in contrast to the conventional DMF, is not a fixed part of the DMF, so it is not designed as a flywheel mass but in the form of a drive plate. It serves only as a connection between the primary mass and the double clutch.

The secondary mass is replaced in this case by the weight of the double clutch, which is fitted on an input shaft (hollow shaft) of the gearbox. There is also no need for the direct bearing connection of the opposed masses, which is realised in the form of ball or plain bearings in the conventional DMF.

Standard DMF for DCT

Image: Standard DMF for DCT
Credit: LuK

1 – tension ring
2 – coupling ring of the double clutch

Another difference from the conventional DMF is the lack of a friction surface on the secondary side. This too is located in the double clutch. There, the central plate bears the friction surfaces for both clutches. Instead of the friction surface on the DMF, an internally toothed flange is used. The coupling ring of the double clutch engages with this flange.

As the two engaging gearwheels would produce noise due to backlash, a tension ring is fitted as a countermeasure. This pre-tensions the two gearwheels so that there is no play between the tooth surfaces. In some models, the tension ring has to be compressed with a special tool before the gearbox is fitted.

Driveplate DMF

DMF with driveplate

Image: DMF with driveplate
Credit: LuK

1 – driveplate

Since 2008, a new gearbox generation has been fitted in some Audi models. These gearboxes can be recognised by the different arrangement of the differential. This is now in front of the clutch in the direction of travel. As a result, the power flow to the left drive shaft has to be transmitted straight through the bell housing by a flanged shaft. Because of this, use of a conventional DMF is no longer possible. In order to equip this drive concept with effective flywheel damping, the DMF with driveplate was developed.

The driveplate is an adapter plate formed from sheet steel, which is riveted on to the DMF at the usual fixing points. The driveplate, like a torque converter in an automatic gearbox, is bolted to the outer radius of the coupling disc on the engine side.

DMF with driveplate - cross-section

Image: DMF with driveplate – cross-section
Credit: LuK

1 – riveted joint
2 – flanged shaft of the gearbox
3 – driveplate
4 – engine coupling disc
5 – DMF

Functions of the driveplate:

  • it provides the space required for the penetration of the flanged shaft
  • it transfers the engine torque via the bolted joint on the coupling disc to the riveted joint on the DMF

Unlike the conventional DMF, the secondary mass has a needle bearing on the gearbox input shaft. This results in a favourable weight distribution between the two flywheels. The internal construction of the DMF is practically identical to that of the other types described.

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